It is known in the art relating to priming of fuel systems (either gasoline or diesel) to completely assemble the entire system and install approximately 5 gallons of fuel in the fuel tank. Then, using the in-tank electric feed pump, the system is primed from the fuel tank, through the fuel feed line, through a fuel rail or diesel injection pump, and then back through the return line to the fuel tank.
In a known fuel system, which includes a fuel filter between the fuel tank and a direct injection diesel fuel injection pump, the prior method of priming is not acceptable. A small orifice in the injection pump housing limits the flow of priming fuel through the system. Further, the fuel filter housing has a top connected inlet and a bottom feeding outlet. A portion of the air in the filter is trapped in the housing above the outlet when fuel is fed in the normal direction from the tank to the injection pump. Particularly when the filter is mounted above the fuel tank in the system, the trapped air allows fuel in the line to the filter to drain back to the fuel tank when the feed pump is shut off. The problem is greater as the filter is mounted higher in the system. When attempting to start the engine thereafter, some of the trapped air is pumped to the inlet of the fuel injection pump, causing it to be air bound and preventing engine starting.
If a vehicle with this known system were to run out of fuel in operation, air in the system would prevent restarting of the engine even after fuel was delivered to the fuel tank. This would require bleeding of the fuel lines to eliminate the trapped air in order to allow engine restart and permit the fuel system to again perform in the desired manner.